Joining SWA and TW&E

[New2Game]

I'm wanting to run a SWA cable to supply an outbuilding. The SWA needs to be 16mm^2 because its a 34M run and I have to take volt drop into equation. Unfortunately the run from the consumer unit to the outside wall is quite a bendy 5M run (up stairs n round corners), so i propse to use TW&E from CU to a galv box which is on the inside of an outside wall, then have the SWA run to this and connect to it from the outbuilding.
Would this sound to be ok and a good installation method?

 

[Lectrician]

I would prefer to go the full length personally.

16mm T+E is going to be fairly hard to route anyway.

I would substitute the 16mm T+E for 16mm Split Concentric.

Join it with a galvanised adaptable box if inside, or a larger gewiss if outside. Fit suitably sized dinrail terminals inside - I would go for 125amp ones (35mm).